1. Field of the Invention
The present invention relates to a light-supplying optical device that can be used, for example, in an image input device that reads image information through photoelectric conversion.
2. Description of Related Art
FIG. 6 shows a conventional image input device. The light-supplying optical device of the image input device is shown in FIG. 7. The light-supplying optical device shown in FIG. 7 has a basic optical arrangement as shown in FIGS. 8A-8B; however, the optical path is altered through the use of two mirrors 102 and 105 to enable its containment within a limited space.
In FIG. 7, two optical path changing mirrors are provided, one of which is comprised of a toric mirror 102. As shown in FIG. 8A, which is a modified top view of FIG. 7, light rays emitted from a light source 103 are reflected by the toric mirror 102, which is provided with a curvature R1 to illuminate a single line of light onto the surface of an original document 101 (such as a transparency, for example). (Actually, as shown in FIG. 7, the light reflected by toric mirror 102 reflects from optical path changing mirror 105, prior to illuminating the original document.) In addition, as shown in FIG. 8B, the image of the light source 103 is formed, by means of a curvature R2, into an image on the surface of the original document 101. The toric mirror 102 uses curvature R1 (which extends in a plane parallel to the surface of the original document 101) to collect the light rays emitted by source 103 in one direction, and uses curvature R2 (which extends in a plane perpendicular to the surface of the original document 101) to collect the light rays emitted by source 103 in a direction perpendicular to the direction in which the light rays are collected by curvature R1.
As shown in FIG. 6, light rays emitted from the light source 103 are incident on the toric mirror 102, at an angle 111 relative to the axis 110 of the toric mirror so that the light rays are reflected toward the subsequent optical path changing mirror 105. The light rays reflected by the toric mirror 102 are formed into an image on the surface of the original document 101 after reflection by the optical path changing mirror 105. This arrangement prevents the light rays between source 103 and toric mirror 102 from interfering with the light rays between toric mirror 102 and optical path changing mirror 105.
The image information of the original document illuminated by the light rays is formed into an image on a linear image sensor 109 (which can be, for example, a charge coupled device CCD) by means of a photographic lens 108, for example. By causing a holder 107 that holds the original document to move in the direction indicated by the arrow A in FIG. 6, all of the information in the original document can be read in succession by the linear image sensor 109.
The light source 103 has the structure shown in FIGS. 9A-9B. A stem 202 is soldered onto a light source base 201. On top of the stem, multiple point light producing components such as LED chips 210a, 210b are arranged in rows, and are bonded to the stem. Around each LED chip is formed a conical reflector 202a that reflects light emitted in the sideways direction from the LEDs and projects the light upward (FIG. 9B) from the LED chips.
In order to emit light in three colors, the light source 103 is composed of two rows of LED chips 210a and 210b, with blue LEDs that produce a small quantity of light per chip arranged in one row 210a (in this example, six LEDs are provided in row 210a) and with the other row 210b comprised of red LEDs and green LEDs arranged in a GRGGRG pattern. The light from LED chips 210a and 210b, after being reflected by the reflector 202a and projected upward from the chips (FIG. 9B), is reflected by a blue-reflecting membrane 205a or by a wholly reflective mirror 205b, formed at a certain angle and with a specified spacing, and is emitted frontwards (to the right in FIGS. 9A and 9B, and to the left in FIG. 6), and is collected by the toric mirror 102 so as to form a line on the surface of the original document as detailed above.
The light emitted from the blue LEDs is reflected by the blue-reflecting membrane 205a, while the light emitted from the red LEDs and green LEDs is reflected by the wholly reflective mirror 205b, so that when viewed from the front of the light source it appears that the three colors of light have all been produced in the same position. Switching between the red, green and blue colors is controlled electrically, making high speed reading of the original document possible.
With the described conventional light-supplying optical device, the incidental light rays form an angle 111 with the axis 110 of the toric mirror so that the light rays 104 emitted from source 103 to toric mirror 102 do not interfere with the light rays reflected by the toric mirror 102 and so that optical path changing mirror 105 does not interfere with the light rays 104 between source 103 and toric mirror 102. However, since the toric mirror has the curvatures R1 and R2, the angle at which the light is reflected differs between the center and the perimeter of the toric mirror 102. As a result, the light image projected on the surface of the original document 101 is bowed instead of being a perfectly straight line, creating the so-called line bow phenomenon.
FIG. 10A illustrates the line-bow phenomenon. Rather than forming a straight line 111a on the original document 101, a bowed line of light 110a is formed on original document 101. Accordingly, the quantity of light (shown in FIG. 10B) read by the image sensor 109 is not linear, with the problem that the quantity of light at the center and at the ends of the read line are not uniform. The graph in FIG. 10B indicates that a uniform amount of light cannot be obtained, because the amount of light at the center of the image sensor is smaller, while the amount of light at the ends of the image sensor is greater.